Pin assembly of an electrode and method of manufacturing the same

ABSTRACT

Disclosed are a pin assembly for providing current to an electrode, e.g. an inert or oxygen evolving anode, and its manufacturing method. The pin assembly is configured to be inserted into an electrode body of an electrode for providing an electric current to the electrode body. The pin assembly comprises a structural support member configured to mechanically support the electrode body, and a protective conductive member configured to embed the structural support member. The protective conductive member comprises at least one metal or alloy thereof adapted for conducting the electric current while protecting the structural support member against corrosion during a given period of time of use of the electrode. The pin assembly enables convenient electrical connection of the electrodes, combines electrical and thermal performance for optimizing cell efficiency, provides structural and corrosion durability for extending pin assembly life, and utilizes robust joining processes for high reliability.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a continuation of PCT/CA2022/050435 filed on Mar. 23, 2022, the content of which is incorporated herein by reference, and which claims the benefits of priority of U.S. Provisional Patent Application No. 63/165,406 filed at the United States Patent and Trademark Office on Mar. 24, 2021, the content of which is also incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to a pin assembly of an electrode and a method for manufacturing the same, more particularly a pin assembly for an anode, such as an inert or oxygen evolving anode, to be used inside an electrolytic cell, for instance for the production of metals, such as aluminum.

BACKGROUND

Aluminum metal, also called aluminium, is produced by electrolysis of alumina, also known as aluminium oxide (IUPAC), in an electrolytic bath of molten electrolyte at about 750-1000° C. contained in a number of electrolytic cells. The cells have a crucible made of a refractory material capable of containing the electrolyte, at least one cathode and at least one anode. The electrolysis current that circulates in the electrolyte through the anodes and cathodes causes alumina reduction reactions and is also capable of maintaining the electrolyte bath at the target operating temperature by the Joule effect. The electrolysis cell is regularly supplied with alumina so as to compensate for consumption of alumina caused by electrolysis reactions.

In the traditional Hall-Heroult process, the anodes are made of carbon and are consumed during the electrolytic reaction. The anodes need to be replaced after 3 to 4 weeks. Consumption of the carbonaceous material releases large quantities of carbon dioxide in the atmosphere. Aluminum producers have been searching for anodes made of non-consumable materials, called “inert anodes” or “oxygen evolving anode”, to avoid environmental problems and costs associated with manufacturing and use of anodes made of carbonaceous material. Replacement of traditional carbon anodes with inert anodes is indeed associated with significant environmental benefits because inert anodes produce no CO₂ or CF₄ emissions. Several materials have been proposed, particularly ceramic materials (such as SnO₂ and ferrites), metallic materials and composite materials such as materials known as “cermets” containing a ceramic phase and a metallic phase, particularly nickel ferrites containing a metallic copper-based phase.

Problems encountered in the development of inert anodes for the production of aluminum by electrolysis lie not only in the choice and manufacturing of the material from which the anode is made, but also in the electrical connection between each anode and the conductor(s) that will be used for the electrical power supply of the electrolytic cell. Generally, an inert anode pin assembly extends from the bottom of a support (e.g. distribution plate) for suspending an anode in an aluminum reduction cell and for providing an electrical path to the anode without allowing excessive cell heat loss. An inert anode is electrically connected to the electrolytic cell, for instance via a conductor rod connected to the inert anode, where the cathode directs the current into an electrolytic bath to produce non-ferrous metal, the current exiting the cell via the anode. Inert anodes are electrically connected to conductors that are typically made of metal such as nickel, Inconel® or steel. However, making a low voltage drop electrical connection between a metallic conductor and an inert anode comprising for instance a ceramic or ceramic-metallic (cermet) is a challenge. The connection must be maintained with good integrity (low voltage drop) over a wide range of temperatures and operating conditions. A low voltage drop electrical connection is important to minimize the cell voltage and energy consumption of the process.

A major challenge in the field of inert anode assemblies and, more particularly conductive rods, is finding materials that can survive in both an oxygen rich and a fluoride rich environment at high temperatures. For instance, a purge gas method has been tested to pressurize a purge space to exclude corrosive species from attacking the structural support and electrical conducting members. However, purging each conductive rod, or pin, typically requires a complex plumbing system and a costly infrastructure for gas delivery. For instance, pin purging may require a pin design that may include a series of concentric tubes through the length of the pin to protect the structural support rod from corrosive species. Furthermore, this type of pin design would be costly to fabricate.

Anodes are not necessarily gas and liquid tight. Anodes can allow both oxygen and fluorides to migrate through the anode walls and enter the anode bore, causing severe corrosion to the electrical connections, and reducing the anode pin, and therefore the anode. After several months, the pins could be corroded through and the anode tops could be split open by the corrosion products.

Several methods and devices have been proposed for the connection of inert anodes, such as those listed in the background section of U.S. Pat. No. 7,544,275, the content of which is incorporated herewith by reference. These solutions present several drawbacks such as making the manufacture of the anodes more difficult by imposing constraints on baking parameters for the active part of the anode, or by imposing perfect control of the process for formation of the intermediate layer and thus complex additional steps. Other solutions known in the art require a chemical reduction of the contact surface before formation of the joints, considerably complicating manufacturing of the anodes and the assembly of the electrical connections.

U.S. Pat. Nos. 4,456,517, 4,450,061, 4,609,249 and 6,264,810 describe mechanical connections applicable to anodes with a central cavity. These connections are sensitive to changes in the mechanical properties of its constituent elements when the anodes are used, and introduce mechanical tensions between the anode and the metallic parts. Moreover, these solutions are sensitive to the corrosive ambient atmosphere of the electrolytic cells. In order to overcome this difficulty, some of these patents also propose to add screens and/or inert filling materials. These complementary protection means complicate the manufacture of connections and make it more expensive. The solution proposed in the above cited U.S. Pat. No. 6,264,810 has the additional disadvantage that it requires a large number of distinct parts that must maintain their mechanical characteristics over a long period of time.

The prior design of inert anode pin assembly utilizes extensive machining and hand processing for enabling numerous design iterations to be tested without need of expensive tooling modification.

Therefore, there is a need for a new design and a new method of manufacturing for an inert pin assembly and for a new anode that overcome the disadvantages of prior art while allowing high volume production with high reliability and durability.

SUMMARY

The shortcomings of the prior art are generally mitigated by a new electrode pin assembly, an electrode containing the pin assembly, and a method of manufacturing the same, preferably used for the electrolytic production of aluminum.

It is first disclosed a pin assembly configured to be inserted into an electrode body of an electrode for providing an electric current to the electrode body. The pin assembly comprises: a structural support member configured to mechanically support the electrode body; and a protective conductive member configured to embed the structural support member, the protective conductive member comprising at least one metal or alloy thereof adapted for conducting the electric current while protecting the structural support member against corrosion during a given period of time of use of the electrode.

According to a preferred embodiment, the structural support member is further configured to mechanically support a refractory component of the electrode.

According to a preferred embodiment, the structural support member comprises titanium, nickel, iron or an alloy thereof. Preferably, the structural support member comprises stainless steel, or a nickel-based alloy such as Inconel®.

According to a preferred embodiment, the protective conductive member is a tube fitting around the structural support member. Preferably, the tube is a bimetal tube having an upper section comprising a first metal and a lower section comprising a second metal, both first and second metals being conductive of said electric current. More preferably, the first metal of the upper section has a lower thermal conductivity than the second metal of the lower section.

According to a preferred embodiment, the upper section and the lower section of the tube are connected together by welding, preferably by inertia or friction welding.

According to a preferred embodiment, the first metal of the bimetal tube comprises titanium, nickel, iron or an alloy thereof, preferably a steel alloy, more preferably a stainless steel alloy, or a nickel based alloy such as an Inconel® alloy, and the second metal of the bimetal tube comprises at least one of cobalt, copper, and/or an alloy thereof.

According to a preferred embodiment, the structural support member comprises a pin longitudinally extending from a pin head, the pin being configured for passing through a central orifice of the tube. Preferably, the pin head is configured to radially extend beyond an external surface of the lower section of the tube for connecting the pin head to a bottom end of the tube formed by the second metal. Preferably, the pin is connected to the upper section of the bimetal tube by staking or welding.

According to a preferred embodiment, the pin assembly as disclosed herein further comprises a metallic form comprising a conductive metal or an alloy thereof. The metallic form comprises a stem longitudinally extending from a bottom end of a cup, the cup being configured for wrapping around the pin head to form an interlocking connection between the form and the pin once the pin is inserted into the tube. The stem of the form is configured to be inserted into an orifice of the electrode body when the pin assembly is operatively connected to the electrode body. Preferably, the metallic form comprises at least one of cobalt, copper and/or an alloy thereof.

According to a preferred embodiment, the cup and the stem of the form are formed as one part.

According to a preferred embodiment, the cup has a circular lateral section with a cup diameter superior than a diameter of the pin head, the form is assembled over the pin head so that the cup extends over of the lower section of the bimetal tube such as to form a radial gap all around the pin head. Preferably, the form is permanently connected to the bimetal tube by a metal forming or forging operation, such as rotary swaging of the radial gap.

According to another preferred embodiment, the cup has an elliptic-like lateral section defining a major axis and a minor axis, the major axis being larger than a diameter of the pin head, the form is then assembled over the pin head so that the cup extends over of the lower section of the bimetal tube such as to form two opposites gaps between the pin head and the cup along the major axis. Preferably, the form is permanently connected to the bimetal tube by a metal forming or forging operation, such as rotary swaging of the two opposite gaps.

According to a preferred embodiment, the cup once permanently connected around the pin head forms a shoulder, the electrode body being supported by the shoulder of the pin assembly when the pin assembly is operatively connected to the electrode.

According to a preferred embodiment, the protective conductive member is configured to form on its external surface a corrosion product adapted for being mechanically constrained without breaking or fracturing. Preferably, the constraining material comprises one of the following: sintered aluminum oxide tube, aluminum oxide powder, castable refractory, copper shot, inert anode material, or sintered tin oxide tube.

According to a preferred embodiment, the electrode is an anode, more preferably, the anode is an inert anode or oxygen evolving anode.

It is also disclosed herein an electrode assembly for the production of aluminum into an electrolytic cell. The electrode assembly comprises: a plurality of electrodes, each of the electrodes comprising an electrode body connected to a pin assembly, the pin assembly being as defined and disclosed herein; and a distribution plate configured for operatively connecting each of the plurality of electrodes via its respective pin assembly for providing an electrical path to the electrodes.

According to a preferred embodiment, the plurality of electrodes are anodes, preferably inert or oxygen evolving anodes. Preferably, the plurality of anodes are vertical anodes extending downwardly from the distribution plate.

According to a preferred embodiment, the electrode assembly further comprises castable cement with a refractory package around the pin assembly of each electrodes, thereby confining corrosion products of the protective conductive member.

According to a preferred embodiment, the electrode assembly further comprises a ceramic tube surrounding at least in part the protective conductive member of the pin assembly for confining corrosion products of the protective conductive member inside the anode body.

It is yet further disclosed a method for the manufacturing of an electrode comprising an electrode body and a pin assembly configured to be inserted into the electrode body of the electrode for providing an electric current to the electrode body. The method comprises:

-   -   a) providing a structural support member configured to         mechanically support the electrode body;     -   b) embedding the structural support member with a protective         conductive member, the protective conductive member comprising         at least one metal or alloy thereof adapted for conducting the         electric current while protecting the structural support member         against corrosion during a given period of time of use of the         electrode; and     -   c) electrically connecting the pin assembly and the electrode         body to form the electrode.

According to a preferred embodiment, the electrode assembly further comprises a ceramic tube surrounding at least in part the protective conductive member of the pin assembly for confining corrosion products of the protective conductive member inside the anode body.

According to a preferred embodiment, the structural support member comprises titanium, nickel, iron or an alloy thereof. Preferably, the structural support member comprises stainless steel, or a nickel-based alloy such as Inconel®.

According to a preferred embodiment, the protective conductive member is a tube, step b) of the method comprising: fitting the tube around the structural support member.

According to a preferred embodiment, the tube is a bimetal tube having an upper section comprising a first metal and a lower section comprising a second metal, both first and second metals being conductive of said electric current. Preferably, the upper section has a lower thermal conductivity than the lower section.

According to a preferred embodiment, the method further comprises before step b), the step of connecting the upper section and the lower section together by welding, preferably by inertia or friction welding.

According to a preferred embodiment, the first metal of the bimetal tube comprises titanium, nickel, iron or an alloy thereof, preferably a steel alloy, more preferably a stainless steel alloy, or a nickel based alloy such as an Inconel® alloy, and the second metal of the bimetal tube comprises at least one of cobalt, copper, and/or an alloy thereof.

According to a preferred embodiment, in step a) of the method, the structural support member comprises a pin longitudinally extending from a pin head, step b) of the method then comprising: passing the pin through a central orifice of the tube. Preferably, the pin head is configured to radially extend beyond an external surface of the lower section of the tube, step b) of the method then comprising: connecting the pin head to a bottom end of the tube formed by the second metal.

According to a preferred embodiment, step b) of the method further comprises: connecting the pin to the upper section of the bimetal tube by staking or welding.

According to a preferred embodiment, the pin assembly further comprises a metallic form comprising a conductive metal or an alloy thereof, the metallic form comprising a stem longitudinally extending from a bottom end of a cup, step b) of the method then further comprises: wrapping the cup around the pin head to form an interlocking connection between the form and the pin once the pin is inserted into the tube; and step c) of the method then comprises: inserting the stem of the form into an orifice of the electrode body for operatively connecting the pin assembly to the electrode body. Preferably, the metallic form comprises at least one of cobalt, copper and/or an alloy thereof.

According to a preferred embodiment, the cup and the stem of the form are formed as one part.

According to a preferred embodiment, the cup has a circular lateral section with a cup diameter superior than a diameter of the pin head, step b) of the method comprising: assembling the form over the pin head so that the cup extends over of the lower section of the bimetal tube such as to form a radial gap all around the pin head.

According to a preferred embodiment, the method further comprises permanently connecting the form to the bimetal tube by a metal forming or forging operation, such as rotary swaging of the radial gap.

According to a preferred embodiment, the cup has an elliptic-like lateral section defining a major axis and a minor axis, the major axis being larger than a diameter of the pin head, step b) of the method comprising: assembling the form over the pin head so that the cup extends over of the lower section of the bimetal tube such as to form two opposites gaps between the pin head and the cup along the major axis.

According to a preferred embodiment, the method further comprises permanently connecting the form to the bimetal tube by a metal forming or forging operation, such as rotary swaging of the two opposite gaps.

According to a preferred embodiment, the step of permanently connecting the form around the bimetal tube comprises forming a shoulder with the cup formed or forged around the pin head, whereby in use, the electrode body is supported by the shoulder of the pin assembly when the pin assembly is operatively connected to the electrode.

According to a preferred embodiment, step c) of electrically connecting the pin assembly to the electrode body comprises:

-   -   installing and aligning in fixture the pin assembly into an         orifice of the electrode body;     -   pouring a first copper shot into the orifice of the electrode         body;     -   optionally, compacting the first copper shot;     -   pouring castable material into the orifice over the first copper         shot; and     -   allowing castable material to cure.

According to a preferred embodiment, the method further comprises pouring a second copper shot above the first copper shot, wherein the second copper shot comprises copper particles smaller in size than copper particles of the first copper shot. Preferably, compacting the copper shots comprises vibrating the electrode body.

According to a preferred embodiment, a lower limit of the castable material is adjacent the shoulder.

According to a preferred embodiment, the protective conductive member is configured to form on its external surface a corrosion product adapted for being mechanically constrained without breaking or fracturing. Preferably, the constraining material comprises one of the following: sintered aluminum oxide tube, aluminum oxide powder, castable refractory, copper shot, inert anode material, or sintered tin oxide tube.

According to a preferred embodiment, the electrode manufactured by the method as disclosed herein is an anode, more preferably the anode is an inert anode or oxygen evolving anode.

Therefore, it is also disclosed herein the use of an electrolytic cell comprising a plurality of electrodes, preferably anodes, more preferably inert or oxygen evolving anodes manufactured by the method as disclosed herein, for the production of metals, such as aluminum.

The present invention allows protecting the structural support pin of the electrodes, such as anodes, from degradation by a cryolite-based molten electrolyte bath of an electrolytic cell, and from HF, O₂ and other gases generated in the electrolytic cell.

The present invention also improves metal production, such as aluminum production, for instance by limiting potential bath and metal contamination by the pin and/or the electrode material.

The present invention also provides an easier method for the manufacturing of a pin assembly and a method for connecting the anode body to the anode assembly in order to obtain an anode protected from degradation during the operation of the electrolytic cell.

The present invention limits breakaway oxidation or breakaway corrosion of the pin so that the utility life of an anode is predictable.

Other and further aspects and advantages of the present invention will be better understood upon the reading of the illustrative embodiments about to be described or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the invention will become more readily apparent from the following description, reference being made to the

FIG. 1 is a side view of the pin assembly in accordance with a preferred embodiment of the present invention;

FIG. 2 is cross-sectional view of the pin assembly of FIG. 1 along line A-A;

FIGS. 3A and 3B are cross-sectional schematic illustrations of the connecting section of the pin assembly illustrated on FIG. 1 , wherein FIG. 3A is a plan view, and FIG. 3B is a perspective view, according to a preferred embodiment;

FIGS. 4A to 4D illustrates different steps (A) to (D) of the connection of the pin assembly to an electrode body, according to preferred embodiments;

FIG. 5 is a cross-sectional partial view of an electrode comprising the electrode body and the pin assembly according to a preferred embodiment; and

FIG. 6 is a sectional view of two different pin assemblies within an inert anode assembly in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A novel electrode pin assembly will be described hereinafter. Although the invention is described in terms of specific illustrative embodiments, it is to be understood that the embodiments described herein are by way of example only and that the scope of the invention is not intended to be limited thereby.

The terminology used herein is in accordance with definitions set out below.

As used herein % or wt. % means weight % unless otherwise indicated. When used herein % refers to weight % as compared to the total weight percent of the phase or composition that is being discussed.

By “about”, it is meant that the value of weight % (wt. %), time, length, volume or temperature can vary within a certain range depending on the margin of error of the method or device used to evaluate such weight %, time, length, volume or temperature. A margin of error of 10% is generally accepted.

The description which follows, and the embodiments described therein are provided by way of illustration of an example of particular embodiments of principles and aspects of the present invention. These examples are provided for the purposes of explanation and not of limitation, of those principles of the invention. In the description that follows, like parts and/or steps are marked throughout the specification and the drawing with the same respective reference numerals or signs.

As aforesaid, a major challenge in the field of inert anode assemblies and, more particularly conductive rods, is finding a material that can survive in both an oxygen rich and a fluoride rich environment.

Disclosed herein is first a pin assembly for an electrode, such as, but not limited to an anode, configured to be inserted into an electrode body of an electrode for providing an electric current to the electrode body. The pin assembly 100, as illustrated on FIGS. 1 and 2 , comprises a structural support member 120 configured to mechanically support the electrode body; and a protective conductive member 110 configured to embed the structural support member. The protective conductive member comprises at least one metal or alloy thereof adapted for conducting the electric current while protecting the structural support member against corrosion during a given period of time of use of the electrode.

According to a preferred embodiment, such as the one illustrated on FIGS. 1 to 3 , the pin assembly 100 may comprise the structural support member 120 embedded into a tube 110 comprising the at least one metal or alloy thereof conducting the electric current.

As illustrated on FIGS. 2, 3A or 3B, the tube 110 defines a circumferential wall 111 surrounding the structural support member 120 for conducting the electric current electricity from the anode body. The circumferential wall 111 of the tube 110 is configured in size to confine the structural support member 120, and as such to protect the structural support member 120 from corrosion during a given period of time of use of the anode.

According to a preferred embodiment, the tube 110 may be a bimetal tube (FIG. 1 or 3 ) with its longitudinal central orifice 113, and having an upper section 112 comprising a first metal and a lower section comprising a second metal 114, both first and second metals being conductive of electric current. Preferably, the metal of upper section has a lower thermal conductivity than the metal of the lower section. For instance, the upper section 112, may comprise steel, and the lower section 114, may comprise cobalt and/or copper, the two sections being preferably connected together by welding, such as inertia or friction welding.

It has to be understood that all metals mentioned in the instant application encompass the metal per se, but also any alloy of said metal, or any composite comprising said metal or alloy, as long as the metals, alloys and composites are conductive of electricity. The present application disclose the use of titanium, nickel, iron, and/or copper, or alloys thereof. Preferably, iron based alloys may comprise steel or stainless steel, and Nickel based alloys may comprise an Inconel® alloy.

As aforesaid, according to a preferred embodiment, inertia welding may be used for manufacturing the bimetal tube. Inertia welding is an economical and reliable process for joining metals in which a rotating work piece is forced against a stationary work piece causing frictional heating at the interface. Advantages include rapid cycle time, minimal surface preparation and no porosity. Also, since heat is rapidly generated directly at the interface, inertia welding is an energy efficient and consistent process that requires no preheating. Another advantage of inertia welding is that dissimilar metals can be joined, even metals having a wide difference in melting points. Copper and steel can be joined by inertia welding for a variety of industries. Furthermore, inertia welding using the actual pin assembly parts have been very successful resulting in a strong bond over the entire interface.

According to a preferred embodiment illustrated on FIG. 3 , the structural support member 120 may comprise a nail-shaped pin 120 having a pin head 122 and a pin or shank 124 extending from the pin head. The pin head 122 is configured to be connected to the bottom end 116 of the lower section 114 of the tube 110 with the shank configured for passing through the orifice 113 of the bimetal tube 110. The shank 124 also connects at the top end 118 of the upper section 112 of the tube by means of, for example, staking or welding. According to the preferred embodiment shown in FIGS. 3A or 3B, the pin head 122 may extend radially, beyond the external surface of the tube's wall 111, abutting as such on the tube's wall. Other configurations to connect and block the structural support member to the tube can be considered. The pin 120 may be fabricated using a wire form process such as the one commonly used for the production of nails and other fasteners.

The pin assembly 100 as illustrated in the drawings also includes a form 130, preferably comprising the same metal or alloy thereof, than the lower section 114 of the bimetal tube 110, such for instance cobalt and/or copper. The form 130 comprises a cup 132, and a long stem or rod 134, extending from the bottom end 136 of the cup 132.

According to a preferred embodiment, the cup 132 and the stem 134 are preferably formed as one part using a process called combination impact extrusion in which a metal cylinder is compressed in a vertical hydraulic press between a lower die having a stepped pin that forms the interior and top end of the cup. In a single stroke, the cylinder is forward extruded into the lower die and backward extruded into the upper die. This is a very fast and material efficient process that also eliminates the cost and associated failure modes of a secondary connection.

According to a preferred embodiment, the form 130 can be then assembled over the pin head 122 so that the cup extends over the lower tube section 114 forming a radial gap (not illustrated). The form 130 is then permanently connected to the bimetal tube 110, for instance by means of rotary swaging, a forging process in which sets of opposing cam-actuated dies repeatedly impact the cup around the circumference to close the radial gap and compress the perimeter wall onto the bimetal tube. The swaged cup 132 also wraps tightly around the pin head 122 to form an interlocking connection so that the walls of the cup. During this process, a shoulder 140 of the pin assembly can be formed adjacent the internal pin head 122 of the pin. The shoulder 140 may be useful for supporting the anode body.

Rotary swaging is very fast, energy efficient, material efficient, and easily automated making it very economical for high volume production. Furthermore, swaging trials of prototype samples indicate that a creeping spindle swaging machine can also be used to produce a gastight joint which, based on earlier testing will lead to the formation of a diffusion bond which is desirable for maintaining electrical continuity, corrosion resistance, and structural integrity of the pin assembly.

According to a preferred embodiment, the section of the cup 132 of the form 130 may be circular, forming a circular gap around the bimetal tube 110 and the pin head 122. Rotary swaging is then applied all around the circumference of the cup 132 to close the gap. Alternatively, the section of the cup of the form can be elliptic-like. The pin head may then be adapted to have a form matching the form of the cup in order to be inserted inside the cup. Rotary swaging is then applied only on the opposite sections forming the gaps, to close the gaps. Although a cup with a circular or elliptic cross-section are disclosed herein, it has to be understood that a cup with a different geometry (e.g. squared, rectangular, orthogonal, etc.) can be used without departing from the scope of the present invention.

Manufacturing Method

A method for the manufacturing of an electrode, such as an anode 200, is illustrated in FIGS. 4A to 4D.

According to a preferred embodiment, the method may comprise the steps of:

-   -   a. inserting the pin assembly 100 into an orifice 220 of the         anode body 210 and aligning the pin assembly and the anode body         in fixtures F1-F2 (FIG. 4A);     -   b. pouring a first copper shot 230 into the orifice 220 of the         anode body 210 (FIG. 4B);     -   c. optionally, pouring a second copper shot 240 into the anode         over the coarse copper 230 (FIG. 4C);     -   d. optionally, compacting each shots after step b or step c, for         instance by vibrating the anode;     -   e. pouring castable ceramic or metallic material 250 into the         anode over the fine copper 240 (FIG. 4D); and     -   f. allowing said castable ceramic or metallic material to cure.

The first and second copper shots can comprise coarse or fine copper particles. Preferably, the first copper shot may comprise coarse copper particles whereas the second copper shot may comprises fine copper particles.

The resulting electrode, such as the anode 200 illustrated in FIG. 5 , may comprise:

-   -   the anode body 210;     -   the orifice 220 of the anode body 210;     -   the pin assembly 100, as the one disclosed herein, inserted and         aligned into the orifice 220 of the anode body;     -   first copper particles 230 poured into the anode orifice;     -   second copper particles 240 poured above the first copper         particles and preferably approximately up to adjacent the         shoulder 140 formed by the swaged cup 132; and     -   the cured castable material 250 above the second copper         particles 240, preferably adjacent the shoulder 140.

As shown in FIG. 5 , the long copper stem 134 connected to the cup 132 forming a shoulder 140 extends into the slot or orifice 220 of the anode. The support pin 120 embedded within the bimetal conductive tube 110, includes a shank 124 extending through the tube 110, the head 122 within the shoulder then extending beyond the tube perimeter for axial support of the shoulder 140.

The upper section 112 of the bimetal tube 110 forms a metallic cylindrical adapter for welding, for instance to an electrical distribution plate 410 of an anode assembly 400 such as the one illustrated on FIG. 6 , and limiting heat loss. The adapter provides both an electrical and structural connection between the pin assembly and the electrical distribution plate.

FIG. 6 shows two different embodiments of the pin assembly inserted and connected into an anode body. The pin assembly on the right of FIG. 6 further comprises another protective tube 300 for surrounding, confining and protecting the pin assembly 100. The other protective tube 300 may comprise alumina or copper, preferably copper confined by refractory castable.

Copper corrosion is not increased by liquid bath or bath vapor. The key mechanism for copper corrosion is oxidation. Therefore, the concentric tubes previously tested for purge gas flow method can be eliminated, giving more room to increase the thickness of the protecting/confining tube 110.

To keep the oxide adherent to the base metal, the copper is confined inside the anode, close to the anode wall, filling the anode with copper shot around the pin and casting cement around the pin through the refractory package, or surrounding the copper pin with a ceramic tube. When copper is confined and allowed to freely oxidize, the oxide product will fill the voids in the confined space, densify, and oxidation is slowed significantly without applying a large load to the confinement material, in this case a ceramic anode, alumina tube, castable cement, or other material. This is due to copper oxidation which is largely driven by outward grain boundary diffusion of copper ions through the oxide layer. Copper, in compression at a high temperature has the capacity to transfer the structural load of the anode and refractory package to the internal structural member, enabling the pin to act both as a structural support and electrical conductor.

Corrosion Field Tests of the Preferred Embodiment and Prior Art

Anode pin assemblies were manufactured and installed into anodes that were then placed in service. That is pin assemblies were supporting the weight of and conducting electricity to anodes undergoing electrolysis. All conditions were the standard conditions as typically found in Applicant's aluminum electrolysis cells. Test times ranged from 0.06 year to >1 year. Both monolithic pins, made of a single material, have been tested together with the preferred embodiment disclosed herein.

For the monolithic design, the corrosion performance of a wide variety of iron-based, nickel-based, and cobalt-based engineering alloys were tested, including all of the 300-series of stainless steels, many Inconel® alloys, and several more exotic (i.e. expensive) alloys with supposedly excellent performance in the presence of oxygen or fluorine. Results of the monolithic, single material pins are given in Table 1 for Inconel® 600 as they are typical of all the iron-based and nickel-based alloys tested. The simple result is that the corrosion rate of these monolithic pins is far too high to be useful for a long-life inert anode.

The corrosion results for the preferred embodiment of the instant application, are also given in Table 1. In this case, it is necessary to give the corrosion rate of both the outer member (copper tube) and the inner core (Inconel® 600 in this case). The average corrosion rate of the outer copper tube in the location of maximum corrosion is 20 times lower than that comparative known technologies. It is also important to note that the standard deviation of the corrosion rate has likewise been reduced by a factor of 10. This is an important finding because a lower standard deviation means that the service life is more predictable. The corrosion rate of the protected structural member was below detectable limits, even after more than 1 year of service.

TABLE 1 Comparison of corrosion rates of anode pins in the location of maximum corrosion: Standard Average deviation of rate of radial rate of radial metal loss metal loss Pin Design Material (in./yr.) (in./yr.) Monolithic metal Inconel 600 1.01 0.27 (Comparative technology) Multicomponent Protective conductive 0.05 0.03 Pin assembly member: Copper (Cu) (present Structural support <0.005 n/a invention) member: Inconel ™ 600 (inside of copper protection)

The results given in Table 1 above assume that the extent of corrosion increases linearly with time. This is a reasonable interpretation of the corrosion data of the monolithic metal, especially for corrosion tests longer than approximately 0.1 years. However, the corrosion of copper members of the preferred embodiment in this environment appear to more closely follow what is known as a parabolic corrosion rate. That is, the extent of copper corrosion is roughly proportional to time squared. More simply, the rate of copper corrosion slows down over time. This strongly suggests that the copper oxide layer remains compact and adherent, likely as a result of its confinement by a strong material such as a castable refractory. Thus, it is believed that the true performance of copper as a protection against corrosion exceeds that shown in Table 1, especially for times longer than 1 year.

The parabolic rate of copper corrosion should be sustained when the corrosion products remain adherent to the base metal. To maintain this adherence, the copper is confined. The copper may be confined by a relatively weak material, such as copper shot if that copper shot is further confined by a stronger material such as a ceramic anode. Alternatively, the copper may be confined with a stronger member such as either a ceramic tube such as alumina or more preferably by a casting a refractory material around it. When confining the copper, it is important to make room for the differential thermal expansion of copper and the confining member. When confining with a tube, the tube can be sized to give a small gap between the copper and tube. When confining with a castable refractory, a thin compliant expansion material should be placed between the two members, as disclosed in US Pat No. 2004/0195091 A1, the content of which is incorporated herein by reference. When copper is thus confined, the corrosion products remain adhered, fill the voids of the confining member (if it is porous) and densify, but do not apply a load large enough to fracture the confining member. The outer-most confining member maintaining this load being a ceramic anode, alumina tube, castable refractory, or other material. However, copper, confined in this manner, can also transfer the structural load of the electrode and refractory package to the inner structural support member, enabling the pin assembly to act both as a structural support and electrical conductor protected from corrosion.

Test results indicate that a stainless steel-reinforced copper conductor can be configured for withstanding structural and environmental stresses while providing electrical and thermal performance for enhancing cell efficiency.

The new designs of the pin assembly disclosed herein reduce the pin down to its simplest components utilizing the key breakthroughs discovered to combat pin corrosion, by using solid metal, such as copper, for protecting the structural member 120 (core). This eliminates all structural member corrosion.

Advantages of the Present Pin Assembly:

-   -   enabling convenient connection to the distribution plate and         anode;     -   combining electrical and thermal performance for optimizing cell         efficiency;     -   providing structural and corrosion durability for extending         anode life; and/or     -   utilizing robust joining processes for high reliability.

While illustrative and presently preferred embodiments of the invention have been described in detail hereinabove, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art. 

What is claimed is:
 1. A pin assembly configured to be inserted into an electrode body of an electrode for providing an electric current to the electrode body, the pin assembly comprising: a structural support member configured to mechanically support the electrode body; and a protective conductive member configured to embed the structural support member, the protective conductive member comprising at least one metal or alloy thereof adapted for conducting the electric current while protecting the structural support member against corrosion during a given period of time of use of the electrode; wherein the protective conductive member is a tube fitting around the structural support member; and wherein the tube is a bimetal tube having an upper section comprising a first metal and a lower section comprising a second metal, both first and second metals being conductive of said electric current.
 2. The pin assembly according to claim 1, wherein the structural support member is further configured to mechanically support a refractory component of the electrode, and wherein the structural support member comprises titanium, nickel, iron or an alloy thereof.
 3. The pin assembly according to claim 1, wherein the first metal of the upper section of the bimetal tube has a lower thermal conductivity than the second metal of the lower section.
 4. The pin assembly according to claim 1, wherein: the first metal of the bimetal tube comprises titanium, nickel, iron or an alloy thereof; and the second metal of the bimetal tube comprises at least one of cobalt, copper or an alloy thereof.
 5. The pin assembly according to claim 1, wherein the structural support member comprises a pin longitudinally extending from a pin head, the pin being configured for passing through a central orifice of the tube, and wherein the pin head is configured to radially extend beyond an external surface of the lower section of the tube for connecting the pin head to a bottom end of the tube formed by the second metal.
 6. The pin assembly according to claim 5, further comprising a metallic form comprising a conductive metal or an alloy thereof, the metallic form comprising a stem longitudinally extending from a bottom end of a cup, wherein the cup is configured for wrapping around the pin head to form an interlocking connection between the form and the pin once the pin is inserted into the tube; and wherein the stem of the form is configured to be inserted into an orifice of the electrode body when the pin assembly is operatively connected to the electrode body, and wherein the cup and the stem of the form are optionally formed as one part.
 7. The pin assembly according to claim 6, wherein the metallic form comprises at least one of cobalt, copper or an alloy thereof.
 8. The pin assembly according to claim 6, wherein the cup has a circular lateral section with a cup diameter superior than a diameter of the pin head, the form is assembled over the pin head so that the cup extends over of the lower section of the bimetal tube such as to form a radial gap all around the pin head.
 9. The pin assembly according to claim 6, wherein the cup has an elliptic-like lateral section defining a major axis and a minor axis, the major axis being larger than a diameter of the pin head, the form is then assembled over the pin head so that the cup extends over of the lower section of the bimetal tube such as to form two opposites gaps between the pin head and the cup along the major axis.
 10. The pin assembly according to claim 6, wherein the cup once permanently connected around the pin head forms a shoulder, the electrode body being configured to be supported by the shoulder of the pin assembly when the pin assembly is operatively connected to the electrode.
 11. The pin assembly according to claim 1, wherein the protective conductive member is configured to form on its external surface a corrosion product adapted for being mechanically constrained without breaking or fracturing, wherein the constraining material comprises one of the following: sintered aluminum oxide tube, aluminum oxide powder, castable refractory, copper shot, inert anode material, or sintered tin oxide tube.
 12. The pin assembly according to claim 1, wherein the electrode is an anode, and wherein the anode is optionally an inert anode or oxygen evolving anode.
 13. An electrode assembly of an electrolytic cell for the production of aluminum, comprising: a plurality of electrodes, each of the plurality of electrodes comprising an electrode body connected to a pin assembly, the pin assembly being as defined in claims 1; and a distribution plate configured for operatively connecting each of the plurality of electrodes via its respective pin assembly for providing an electrical path to the electrodes.
 14. The electrode assembly according to claim 13, wherein each of the plurality of electrodes are an anode, wherein the anode are optionally inert or oxygen evolving anodes.
 15. A method for the manufacturing of an electrode comprising an electrode body and a pin assembly configured to be inserted in the electrode body of the electrode for providing an electric current to the electrode body, the method comprising: a) providing a structural support member configured to mechanically support the electrode body; b) embedding the structural support member with a protective conductive member, the protective conductive member comprising at least one metal or alloy thereof adapted for conducting the electric current while protecting the structural support member against corrosion during a given period of time of use of the electrode; and c) electrically connecting the pin assembly and the electrode body to form the electrode; wherein the protective conductive member is a bimetal tube having an upper section comprising a first metal and a lower section comprising a second metal, both first and second metals being conductive of said electric current, step b) then comprising: fitting the bi-metal tube around the structural support member.
 16. The method according to claim 15, wherein the upper section has a lower thermal conductivity than the lower section, the method further comprising before step b), the step of connecting the upper section and the lower section together by welding.
 17. The method according to claim 15, wherein in step a), the structural support member comprises a pin longitudinally extending from a pin head, step b) of the method then comprising: passing the pin through a central orifice of the bi-metal tube.
 18. The method according to claim 17, wherein the pin head is configured to radially extend beyond an external surface of the lower section of the bi-metal tube, step b) of the method then comprising: connecting the pin head to a bottom end of the bi-metal tube formed by the second metal.
 19. The method according to claim 18, wherein the pin assembly further comprises a metallic form comprising a conductive metal or an alloy thereof, the metallic form comprising a stem longitudinally extending from a bottom end of a cup, step b) of the method then further comprising: wrapping the cup around the pin head to form an interlocking connection between the metallic form and the pin once the pin is inserted into the tube; and step c) then comprises: inserting the stem of the metallic form in an orifice of the electrode body for operatively connecting the pin assembly to the electrode body; wherein the cup and the stem of the metallic form are optionally formed as one part.
 20. The method according to claim 19, wherein the cup has a circular lateral section with a cup diameter superior than a diameter of the pin head, step b) comprising: assembling the metallic form over the pin head so that the cup extends over of the lower section of the bimetal tube in order to form a radial gap all around the pin head, and permanently connecting the metallic form to the bimetal tube by a metal forming or forging operation of the radial gap; or wherein the cup has an elliptic-like lateral section defining a major axis and a minor axis, the major axis being larger than a diameter of the pin head, step b) comprising: assembling the metallic form over the pin head so that the cup extends over of the lower section of the bimetal tube in order to form two opposites gaps between the pin head and the cup along the major axis.
 21. The method according to claim 15, wherein step c) of electrically connecting the pin assembly to the electrode body comprises: installing and aligning in fixture the pin assembly into an orifice of the electrode body; pouring a first copper shot into the orifice of the electrode body; optionally, compacting the first copper shot; pouring castable material into the orifice over the first copper shot; and allowing castable material to cure.
 22. The method according to claim 21, further comprising pouring a second copper shot above the first copper shot, wherein the second copper shot comprises copper particles smaller in size than copper particles of the first copper shot.
 23. The method according to claim 15, wherein the electrode is an anode, wherein the anode is optionally an inert anode or oxygen evolving anode. 